1. Field of the Invention
The present invention relates to a method of controlling a semiconductor memory card system and, more particularly, to a control method of communicating warning information in a semiconductor memory card system.
2. Description of the Related Art
Semiconductor memory cards such as SD™ memory cards are widely used in electronic devices such as digital cameras, portable music players, and personal computers as media to store, e.g., image data, music data, and information data. A semiconductor memory card uses a nonvolatile semiconductor memory such as a flash memory. A typical example is a NAND flash memory.
A flash memory such as a NAND memory erases/writes data in blocks with a predetermined size. If the number of times of data erase/write of one block is greater than a predetermined reference value, the reliability of data write in that block may be lowered, or the block may become unusable in some instances.
A semiconductor memory card such as an SD memory card has several spare blocks, in general. This prevents the card itself from becoming unusable even when some unusable blocks (acquired defective blocks) occur. Additionally, a semiconductor memory card uniformly distributes erase/write blocks throughout the semiconductor memory device in the card, instead of concentrating the erase/write blocks to specific blocks.
However, if a user uses a single card for a long time, data rewrite in the card may be done an enormous number of times, and the reliability of stored data may lower. If the number of defective blocks increases, the card itself may become unusable.
A conventional nonvolatile semiconductor memory has a function of causing the semiconductor memory device itself to count the number of times of rewrite and, if it is greater than a maximum rewritable count, outputting a warning signal, as disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 7-65592. A semiconductor memory card disclosed in, e.g., Japanese Patent Laid-Open No. 2003-85054 has spare blocks (redundant blocks). This semiconductor memory card has a function of turning on a built-in light emitting diode (LED) to warn the user if the number of remaining spare blocks becomes less than a predetermined value after data rewrite.
The semiconductor memory device or semiconductor memory card itself has the above-described functions. However, either the semiconductor memory device or the semiconductor memory card has no means for communicating the warning to a host device such as a digital camera incorporating them.